Shaft assembly of a gas turbine engine and method of controlling flow therein

ABSTRACT

A gas turbine engine comprises a shaft assembly including a hollow shaft of the gas turbine engine and a plug connected to the inlet end of the shaft. The hollow shaft has a shaft bore having a bore diameter. The hollow shaft has an inlet end for receiving a first portion of an incoming air flow. The plug has a plug bore therethrough, and an inlet end having an inlet diameter. The inlet diameter of the plug is smaller than the bore diameter. The plug includes a deflection surface adapted to deflect a second portion of the incoming air flow away from the shaft bore. A plug for connecting to an end of a hollow shaft of a gas turbine engine and s method of controlling a flow of fluid through a shaft having a bore therethrough of a gas turbine engine are also presented.

TECHNICAL FIELD

The application relates generally to gas turbine engines and, moreparticularly, to cooling of shafts of gas turbine engines.

BACKGROUND OF THE ART

Gas turbine engines includes hot sections and cold sections. Cold airfrom the cold sections may be used to cool components of the gas turbineengine in a vicinity of the hot section, or components which may heat upduring their use. To enable cooling, the cold air is redirect towardthese components. In some cases, the cool air needs to be shared betweencomponents. Some components may receive more air than needed while othermay not receive enough.

SUMMARY

In one aspect, there is provided a gas turbine engine comprising: ashaft assembly comprising: a hollow shaft of the gas turbine engine, thehollow shaft having a shaft bore having a bore diameter, the hollowshaft having an inlet end for receiving a first portion of an incomingair flow; and a plug connected to the inlet end of the shaft, the plughaving a plug bore therethrough, the plug having an inlet end having aninlet diameter, the inlet diameter of the plug being smaller than thebore diameter, the plug including a deflection surface adapted todeflect a second portion of the incoming air flow away from the shaftbore.

In another aspect, there is provided a plug for connecting to an end ofa hollow shaft of a gas turbine engine, the plug comprising: a plug bodyhaving a first end and a second end, the first end being adapted to beconnected to the hollow shaft; a bore extending through the body fromthe first end to the second end, the first end having a first innerdiameter larger than a second inner diameter of the second end; and aflaring deflection surface disposed on an outer surface of the plug bodybetween the first end and the second end.

In a further aspect, there is provided a method of controlling a flow offluid through a shaft having a bore therethrough of a gas turbineengine, the method comprising: allowing a first portion of an incomingflow through an inlet of a hollow plug connected to the shaft, the inlethaving a diameter smaller than a diameter of the bore of the hollowshaft; and directing a second portion of the incoming flow away from theshaft via a deflection surface of the plug.

DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying figures in which:

FIG. 1 is a schematic cross-sectional view of a gas turbine engine;

FIG. 2 is a schematic of a portion of the gas turbine engine of FIG. 1located toward a turbine section shown with a first embodiment of acontrol plug for a hollow shaft of the turbine section;

FIG. 3 is an isometric view of the control plug of FIG. 2;

FIG. 4 is a schematic of the portion of the gas turbine engine of FIG. 2shown with a second embodiment of the control plug; and

FIG. 5 is a flow chart of method of controlling fluid flow using theplug of any of FIGS. 2 to 4.

DETAILED DESCRIPTION

FIG. 1 illustrates a gas turbine engine 10 of a type preferably providedfor use in subsonic flight, generally comprising in serial flowcommunication a compressor section 14 for pressurizing the air, acombustor 16 in which the compressed air is mixed with fuel and ignitedfor generating an annular stream of hot combustion gases, and acompressor turbine section 18 for extracting energy from the combustiongases. A power turbine shaft 20 supports a plurality of turbine rotors(one power turbine rotor 19 being shown).

Referring to FIG. 2, the power turbine shaft 20 is hollow and has a bore22 extending therethrough. The bore 22 can be used to cool the shaft 20.The bore 22 has a diameter D1 constant throughout a length of the shaft20. It is however contemplated that the bore 22 could have a variablediameter. An inlet end 23 of the shaft 20 facing a compressor turbinebolt 21 comprises a plug 30 (shown in a first embodiment) which controlsan amount of fluid 27 flowing through the bore 22. In the embodimentdescribed herein, the fluid flow 27 is cool air originating from amiddle section of the compressor 14. The compressor turbine bolt 21directs a first portion 27 a of this relatively cool fluid flow 27toward the bore 22 of the hollow shaft 20 so as to cool the shaft 20.The first portion 27 a may not only to cool the shaft 20 but also coolthe entire power turbine rotor 19 (including rotor blades and discsupporting the blades).

The plug 30 additionally deflects a second portion 27 b of the incomingflow 27 away from the bore 22 and redirects it toward a hotter sectionof the compressor turbine section 18 also for cooling purposes. The flow27 arriving from the compressor turbine bolt 21 has a relative highvelocity of the flow 27, and majority of the flow 27 naturally becomesthe first portion 27 a flowing through the shaft 20. To counter thisphenomenon, the plug 30 is designed to deflect the second portion 27 bof the relative high velocity flow 27 radially away from the shaft 20 tocool an upstream face 19 a of the turbine rotor 19.

Turning to FIG. 3, the plug 30 may include a unitary monolithic plugbody 32 made of a material sustaining temperature typically found inthat section of the gas turbine engine 10. It is contemplated that theplug 30 could be made of several connected parts. The plug body 32includes a first end 34, a second end 36, and a bore 38 extendingthrough the body 32 from the first end 34 to the second end 36. Thesecond end 36 is an inlet end of the plug 30 relative to the fluid flow27 and is adapted to face the compressor turbine bolt 21. As will bedescribed below, a size of the inlet is determined to allow only afraction of incoming fluid 27, i.e. first portion 27 a, to flow throughthe shaft bore 22. The second end 36 has a rounded edge which allows asmoother contact with the incoming fluid 27. The first end 34 hasthreads 35 engageable with tapping 24 of an inside of the shaft 20 (bestshown in FIG. 2) for securing the plug 30 onto the shaft 20. It iscontemplated that the plug 30 could be threaded to an outside of theshaft 20. FIG. 4 shows a second embodiment of a plug 30′ having similarcharacteristics to the plug 30 but connecting to the outside of theshaft 20 at threads 25′. In the embodiment shown in FIG. 4, the plug 30′is integrated with a turbine nut 26′. The turbine nut 26′ retains theturbine disc 21 on the shaft 20. It is contemplated that the plug 30could not have the threads 25 and be connected to the shaft 20 by othersuitable means. The plug 30 could, for example, be welded to the shaft20, force fitted, machined integrally within the shaft 20, brazed,axially retained by lugs and slots.

As best shown in FIG. 2, the bore 38 of the plug 30 may have a variablediameter. The bore has a diameter D2 at the first end 34 and a diameterD3 at the second end 36. The diameter D2 is larger than the diameter D3,yet the diameter D2 is smaller than the diameter D1 of the shaft 20. Itis contemplated that the bore 38 could have a constant diameter. Thebore 38 further includes a fairing portion 39 extending from the firstend 34 toward the second end 36. The fairing portion 39 is designed toallow a smooth flow transition for the fluid 27 a flowing from thesecond end 36 to the first end 34. It is contemplated that the fairingportion 39 could be omitted.

The plug 30 also includes a deflection surface 40 on an outer surfacethereof. In the particular embodiment shown in the Figures, thedeflection surface 40 is flaring and concave or frustroconical with thesecond end 36 centrally located, extending outwardly from the second end36 toward the first end 34. The deflection surface 40 is adapted todeflect a portion of fluid 27, i.e. second portion 27 b, away from theshaft bore 24. A shape of the deflection surface 40, and morespecifically its curvature, is determined to direct the second portion27 b toward a predetermined location. In one embodiment, the deflectionsurface 40 has a curvature which deflects the second portion 27 b of theincoming flow 27 toward a first disc of the compressor turbine section18 disposed at proximity of a hot section. It is contemplated that thedeflection surface 40 could be flaring yet not be concave. Thedeflection surface 40 could have any shape that may be optimised fordirecting a portion of a flow in a desired direction. The optimisationmay depend on one or more of the following factors: proportion ofincoming flow to deflect, velocity of the incoming flow, direction todeflect toward. It is also contemplated that the deflection surface 40not be flaring at all. For example, the deflection surface 40 could beflat. The deflection surface 40 may include a plurality of grooves whichmay be designed to reduce swirl.

In the particular embodiment shown in the Figures, the plug 30 includesa grasping portion 42 disposed between the threads 25 and the deflectionsurface 10. The grasping portion 42 facilitates the manipulation of theplug 30 during threading and tightening of the plug 30 against the shaft20. The grasping portion 42 has an hexagonal shape mating that of awrench. It is contemplated that the grasping portion 42 could be omittedor could have a shape different from the one shown in the figures.

Turning now to FIG. 5, a method 50 of controlling the fluid flow 27through the shaft 20 will now be described.

The method 50 starts at step 52 with allowing the first portion 27 a ofthe incoming flow 27 through the second end 36 of the plug 30 connectedto the shaft 20. In one embodiment, the first portion 27 a is apredetermined amount of fluid in order to cool the shaft 20. To allowonly a controlled portion, i.e. the first portion 27 a, through theshaft 20, the plug 30 is disposed at the inlet end 23 of the shaft 20.By choosing a specific inlet diameter D3 of the plug 30, one may controlthe amount of fluid going through the shaft 20. To determine D3, theminimum fluid flow 27 a required to cool the hollow shaft 20 is firstdetermined. Alternatively, one may set a determine a fluid flow otherthan the minimum fluid 27 a required to cool the hollow shaft 20. Forexample, one may determine a fluid flow that exceeds by 10% the minimumfluid required to cool the hollow shaft 20. Once the fluid flow 27 a isdetermined, a diameter corresponding to that fluid flow 27 a isdetermined. That diameter is determined to be the diameter D3corresponding to the plug 30 chosen to be fitted onto the shaft 20.

From step 52, the method 50 goes to step 54, where the second portion 27b of the incoming fluid 27 is deflected away from the shaft 20 by thedeflection surface 40. In one embodiment, the second portion 27 b is apredetermined amount of fluid in order to cool a portion of the engine10 other than the shaft 20. The step 54 happens at the same time as thestep 52. The deflection of the second portion 27 b is enabled by thedeflection surface 40 of the plug 30. The deflection surface 40 isshaped to orient the incoming flow 27 toward a desired component of theengine 10. While the choice of diameter D3 has been determined above infunction of the required fluid flow 27 a to cool the hollow shaft 20, itis contemplated that the choice of diameter D3 could be resulting fromthe choice of fluid flow 27 b to cool a component other than the hollowshaft 20. In one embodiment, the choice of diameter D3 is a compromisebetween the required fluid flow 27 a to cool the hollow shaft 20 andrequired fluid flow 27 b to cool a component other than the hollow shaft20.

Depending on the characteristics of the plug 30, the incoming flow 27may be divided in more or less equal portion. In one embodiment, thefirst portion 27 a represents 70% of the incoming flow 27, while thesecond portion 27 b represents 30% of the incoming flow 27. Otherproportions are contemplated. The plug 30 is designed to split the flow27 into an amount allowing the shaft 20 and the power turbine rotor 19to be cooled but also and deflect a remaining amount to the upstreamface 19 a of the power turbine rotor 19. This flow split is configuredto optimize the cooling of various components of the power turbine rotor19 (rotor blades, disc). In addition, this flow split is configured tooptimize the pressures in the various cavities surrounding the disc,rotor blades and the vane (not shown) and to minimize possibilities ofhot gas path ingestion into those cavities.

With the above plugs and method, the flow of cool air through the shaftis controlled. Only a minimum amount of air needed to cool the shaft canbe directed to the shaft, while another portion of the cool air can bediverted to other components for cooling and pressure management. Theplug is easily installable and its specification can be adapted to anyshaft and environment of the shaft to ensure optimum air redistribution.

The above description is meant to be exemplary only, and one skilled inthe art will recognize that changes may be made to the embodimentsdescribed without departing from the scope of the invention disclosed.For example, the plug could be adapted to hollow shafts of the gasturbine engine other than a turbine shaft. Still other modificationswhich fall within the scope of the present invention will be apparent tothose skilled in the art, in light of a review of this disclosure, andsuch modifications are intended to fall within the appended claims.

The invention claimed is:
 1. A gas turbine engine comprising: a shaftassembly comprising: a hollow shaft of the gas turbine engine, thehollow shaft having a shaft bore having a bore diameter, the hollowshaft having an inlet end for receiving a first portion of an incomingair flow; and a plug connected to the inlet end of the shaft, the plughaving a plug bore therethrough, the plug having an inlet end having aninlet diameter, the inlet diameter of the plug being smaller than thebore diameter, the plug including a deflection surface adapted todeflect a second portion of the incoming air flow away from the shaftbore.
 2. The gas turbine engine as defined in claim 1, wherein thedeflection surface is on an outer surface of the plug and faces awayfrom the shaft in order to deflect a second portion of the incoming airflow away from the shaft bore.
 3. The gas turbine engine as defined inclaim 1, wherein the plug is threaded to one of an inside and an outsideof the inlet end of the shaft.
 4. The gas turbine engine as defined inclaim 1, wherein the inlet end of the plug extends upstream of theshaft.
 5. The gas turbine engine as defined in claim 3, wherein thedeflection surface of the plug is flaring outwardly from the inlet endtoward the shaft.
 6. The gas turbine engine as defined in claim 1,wherein the plug further comprises a grasping portion disposed betweenthe shaft and the deflection surface of the plug.
 7. The gas turbineengine as defined in claim 6, wherein the grasping portion is hexagonalin cross-section.
 8. The gas turbine engine as defined in claim 1,wherein the plug bore includes a fairing portion extending from theinlet end of the plug toward the shaft.
 9. The gas turbine engine asdefined in claim 1, wherein the plug is a power turbine plug and theshaft is a power turbine shaft.
 10. The gas turbine engine as defined inclaim 1, wherein the inner diameter of the plug at the inlet endcorresponds to a diameter providing a minimum flow rate of incomingfluid to the shaft bore for cooling the shaft.
 11. The gas turbineengine as defined in claim 1, wherein the plug bore is coaxial with theshaft bore.
 12. A method of controlling a flow of fluid through a hollowshaft having a bore therethrough of a gas turbine engine, the methodcomprising: allowing a first portion of an incoming flow through aninlet of a hollow plug connected to the shaft, the inlet having adiameter smaller than a diameter of the bore of the hollow shaft; anddirecting a second portion of the incoming flow away from the shaft viaa deflection surface of the plug.
 13. The method as defined in claim 12,wherein directing the second portion of the incoming flow via thedeflection surface of the plug comprises directing the second portion ofthe incoming flow via the deflection surface flaring outwardly from theinlet of the plug.
 14. The method as defined in claim 12, whereinallowing the first portion of the incoming flow through the inlet of thehollow plug includes allowing a majority of the incoming flow throughthe inlet of the hollow plug.